Knee Pain and Swelling in a 44-Year-Old Woman

For a woman of her age and medical history with a weight problem, early osteoarthritis might not be an unreasonable diagnosis for knee pain and swelling after treadmill walking. But in rheumatology, things are so often not what they seem at first glance. What is your diagnosis?

A 44-year-old Hispanic woman presented with left knee pain and swelling of[[{"type":"media","view_mode":"media_crop","fid":"23273","attributes":{"alt":"","class":"media-image media-image-right","id":"media_crop_2188643697637","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"1811","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"float: right; margin: 5px;","title":" ","typeof":"foaf:Image"}}]] 24 hours' duration, after walking on a treadmill as part of a weight-loss program. Pain was localized to the left knee and worsened with weight bearing.

This was not her first episode of knee pain. Nine years earlier, she had sustained an injury to her left knee while loading boxes onto a truck. The resulting pain and swelling of the knee resolved within 24 hours without intervention. Since then, she has had similar recurring episodes of pain and swelling.

Her medical history includes hypertension, hyperlipidemia, gastroesophageal reflux disease, and a pulmonary embolus. Her only medication is daily aspirin. She smokes cigarettes but has no history of alcohol use or recent travel.

The knee showed moderate effusion, mild warmth, and tenderness. Plain radiographs showed increased density in the suprapatellar pouch with normal joint spaces.

Aspiration of her left knee produced 50 mL of yellow blood-tinged fluid, and synovial fluid analysis showed a white blood cell count of 2750/uL with 77% neutrophils and a red blood cell count of 7950/uL with no evidence of crystals.

An MRI scan is at upper right. Can you guess the diagnosis?

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